Question

Which of the following is true with respect to Echeneis?
A. The head resembles a hammer
B. It is a cartilaginous fish
C. Dorsal fin is modified into an adhesive disc
D. Spines are present in second dorsal and anal fins

Answer 1

Hint: Echeneis is a genus of fish belonging to the Echeneidae family of remoras. The Atlantic, Pacific, and Indian Oceans are all home to this genus.
The generic name Echeneis comes from the Greek words echein, which means "to hold", and naus, which means "ship", referring to the fish's capacity to cling themselves to the hulls of ships and, according to tradition, slow them down.
Remoras are big grey parasitic fish that live on the flanks of sharks, manta rays, and other giant fish. Remoras do not pose a threat to their hosts. They just hook themselves to the larger animal and ride along. The remora is harmless as long as the diver is wearing a wetsuit.

Complete answer:
Option A: To maintain suction, these fish have a circular disc on their heads with flexible membranes.
So, option A is not correct.
Option B: The spiny part of the dorsal fin is changed into a flat oval sucking plate on the top of the head and neck, consisting of a double pair of cartilaginous cross plates with serrated free edges, which distinguishes remoras from all other fishes.
So, option B is not correct.
Option C: The most distinguishing feature of Echeneis is its greatly modified dorsal fin, which is an oval-shaped sucking disc. To get food, they attach themselves to sharks, turtles, whales, and huge bony fish. Sharksuckers is another name for them.
So, option C is correct.
Option D: The spiny section of the dorsal fin is transformed into a flat oval sucking plate, composed of a double set of cartilaginous cross plates with serrated free edges, and located on the top of the head and neck, distinguishing remoras from all other fishes.
So, option D is incorrect.

So, option C is the correct answer.

Note:
These are real jawed vertebrates having breathing, excretion, and blood circulation organs. Poikilotherms are creatures that are incapable of regulating their own body temperature. Basically, all fish fall into this category.
Characteristics of pisces-
In most cases, the body is streamlined. Some have a body that is spindle-shaped or elongated.
Their body is divided into three sections: head, trunk, and tail.
The gills aid with breathing.
Blood circulation is observed to be of the closed type.
Bony or cartilaginous internal skeleton.
These are organisms with a cold blood supply.
They can be herbivores or carnivores, oviparous or ovoviviparous, and oviparous or ovoviviparous.